Philips PM5781 Teardown

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PM5781 Programmable pulse generator 125MHz transition times 2nS-100mS

This is a fairly rare instrument, so I took the opportunity to take some photos of the inside during the maintain.
I previously had a PM5786B, which I later sold, and I did a teardown here. Needless to say, internally they're two completely different beasts.
I had already posted the user manual some time ago on the ko4bb and electronics and book websites.
Now I'm looking for the service manual with the schematics and calibration instructions.
Since the battery was replaced by the seller only AFTER the previous one was completely empty, all calibration data was lost.
Unfortunately, this version does not have the PM9579 board that allows for self-calibration.

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Here you can see, in addition to the cursed BR2032 battery, the only custom IC of the instrument, a Philips OQ0501P.

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More Pics...

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More pics... and some resistors need replacing...

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.... an more

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As you can see, many calibrations must be done manually using trimmers. Software calibration likely only works within certain limits,
beyond which, manual adjustments must be made.

[MadTux]

So it's synthesized pulse generator or just like HP8112/8116, analog crap with digital front end ;-)

[coromonadalix]

check here, maybe some similarities

http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Philips/PM5786_125MHz_Pulse_Generator

grab  all you can

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So it's synthesized pulse generator or just like HP8112/8116, analog crap with digital front end ;-)

It certainly has nothing to do with the HP 8116A.
Compared to the HP 8112A, it has superior performance.
But it's an old instrument also, and it's rare.

[coromonadalix]

yes theses are old  but practical, mostly for the fast rise time

wavetek had or have a few possible contender ...

GW Instek had one   not as capable ...

[AVGresponding]

Very, very nice. Made in Sweden, so by the branch of Philips that became Pendulum Instruments.

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Very, very nice. Made in Sweden, so by the branch of Philips that became Pendulum Instruments.

I wonder if they kept the old documentation.
Here in Italy, the Fluke division that distributed these instruments, sent all the documentation from that period to the landfill.
So I can forget about finding the service manual there.

[AVGresponding]

Very, very nice. Made in Sweden, so by the branch of Philips that became Pendulum Instruments.

I wonder if they kept the old documentation.
Here in Italy, the Fluke division that distributed these instruments, sent all the documentation from that period to the landfill.
So I can forget about finding the service manual there.

 

[the Chris]

I also see four shiny blue Philips caps that surely are down in capacitance and up in resistance. If this instrument is from the 90s, they just might lack only 20% of their original specification but so far I've never encountered one of these that got an undeserved replacement.

The instrument looks nicely made, I never saw one before but that just confirms its rarity.

[AVGresponding]

I also see four shiny blue Philips caps that surely are down in capacitance and up in resistance. If this instrument is from the 90s, they just might lack only 20% of their original specification but so far I've never encountered one of these that got an undeserved replacement.

The instrument looks nicely made, I never saw one before but that just confirms its rarity.

The axial ones? AKA "Blue Bastards", I've had them so dry and dead they read OC and tinkle like a bell when you drop them. Dead caps on the display board aren't likely to have caused a 3 or 5 watt output resistor to burn up though. Shorted output transistor/s maybe?

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The resistors were overloaded, probably because DC or RF was inserted into the output, only the 82.5 ohm resistor changed value.
But despite this, there was no damage to the HF amplifiers (fortunately). Everything works normally, except for the lost calibration.
Yes, I'll have to replace some electrolytic capacitors, that was planned. According to the date code on the most recent components, the instrument is from 1992.

The instrument is truly well-engineered: the various PCBs can be lifted and held in place using special guides: an exemplary job.

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Finally, the last pic: it's the PM9579 board (Measurment Interface Unit), which my instrument doesn't have. Self-calibration is possible with this one.
It's located above the CPU board, the one you see in the third pic.
It's not difficult to clone, and the components are common except for a few ECL IC.

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This schematic will probably only be of interest to less than five people on the entire planet (some of the owners of this instrument  ) but I'm posting here anyway the reverse engineering of the PM9579 board mentioned in the previous post.